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Cassiniís journey at Saturn continues with Rev 56, its 57th orbit of the ringed planet. Cassiniís slate of observations this orbit includes distant encounters with Rhea and Titan, a movie sequence of clouds in Saturnís north polar region, and numerous observations of Saturnís rings and small moons. Cassini begins Rev56 on January 9 at its farthest distance from Saturn, called apoapsis. At this point, Cassini is 1.82 million km (1.13 million mi) from Saturn. The first week of Rev56 is filled with observations of Saturnís north polar region, rings, and small satellites. Two small satellite observation sequences are planned for January 10 and 12, including a 13-hour long observation of the co-orbital satellite Janus. The observations are designed to study the orbits of these objects and how they might evolve over short time periods due to perturbations from the other satellites in the system. In addition to the small satellites orbiting in the inner part of the Saturnian system, Cassini will also observe the outer satellite Ijiraq on December 14. Three sequences, planned for January 12 through 14, are dedicated to examining clumps in the F ring. On January 13 and 14, fourteen observations are planned of Saturnís north polar region. The images from these sequences will be examined to better understand cloud motions in the east-west flowing jets in this area. Cassini reaches periapse, the closest point in its orbit, on January 15 when the spacecraft is 199,000 km (124,000 mi) above Saturnís cloud tops. On January 16, Cassini performs three imaging sequences of Saturnís ring system: first of a ringlet in the C ring, then a scan across the ring system from the inner D ring to the outer F ring using the narrow- and wide-angle cameras. Next, Cassini performs three imaging sequences of Rhea with the spacecraft nearly between the Sun and the icy moon, providing an opportunity to observe Rheaís opposition surge. On January 17, two more imaging sequences are planned for Saturnís ring system, observing ringlets in the C ring, the outer A ring (with Atlas), and the F and G rings. A mutual event observation is also planned, wherein Janus transits across Dioneís north pole, though the transit will be obscured by Saturnís rings. The last four days of Rev56 are filled with observations of Saturnís small, inner satellites, as part of the imaging teamís orbital evolution campaign. In addition to these sequences, observations of Titan and the F ring are also planned. The distant observation of Titan, planned for January 20, will show the northern leading hemisphere, including the best observation to date of Menrva, a 400-km wide impact basin in northwestern Fensal. Finally, two calibration sequences are planned to study the narrow-angle cameraís dark-current response (or electronic ďnoiseĒ in the camera system) and the camera's sensitivity.
Cassini begins the following orbit, number 58 (Rev57), on January 21. Rev57 includes distant flybys of Titan and Tethys.